As a storm rolled across central Minnesota Thursday evening, eyes (and cell phone cameras) were turned to the sky as mammatus clouds started forming.

These lumpy bumpy clouds are a weather phenomenon caused by warm air moving up and cold air falling down, creating pockets in the clouds that look like pillowy bumps.

These clouds are a rare example of clouds in sinking air, as most clouds form in rising air. A popular misconception about this cloud type is that they mean a tornado is forming. They get associated with thunderstorms, but they are essentially upside-down clouds. Instead of the fluffy on top clouds we are used to seeing, these ones are fluffy on the bottom due to the reversal of the airflow.

Did you get some cool photos of the mammatus clouds during the storm? Send them our way on our mobile app!

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